1. Field of the Invention
The present invention relates to a light emitting device for emitting a light by utilizing the organic electroluminescence (as will be shortly called as the “EL”) phenomenon and, more particularly, to a light emitting device capable of performing an open/short inspection reliably on a plurality of wires interposed of pixels.
2. Background Art
In recent years, the organic EL display for displaying an image by utilizing the organic EL phenomenon has been noted as one of flat panel displays. This organic EL display is utilizes the light emitting phenomenon of the organic light emitting elements themselves so that it is excellent in a wide angle of visibility and a low power consumption. Especially, the organic EL display is thought to have a sufficient responsiveness to high-speed video signals of high fineness, and its development has been progressed for practices in the image field or the like.
The organic EL display of the active matrix type is constituted such that a drive panel, which is provided with organic light emitting elements and drive elements (i.e., TFT: Thin Film Transistors) for driving the organic light emitting elements, and a sealing panel are arranged to confront each other and are adhered to clamp organic light emitting elements through adhesive layers.
As transistors to compose the organic EL display of the active matrix type, there are needed at least switching transistors for controlling the brightness of pixels and drive transistors for controlling the light emissions of organic EL elements. It is known that the threshold voltage shifts if the voltage is continuously applied to the gate electrodes of the thin film transistors. However, the drive transistors of the organic EL display have to be continuously fed with the electric current while they are causing the organic EL elements to emit lights, so that the threshold shift is easy to occur. When the threshold voltage of the transistors shifts, the current flow through the transistors fluctuates so that the light emitting elements change their brightness.
In most cases, therefore, circuits for controlling the threshold shifts of the thin film transistors have to be formed in the pixels so that the numbers of elements and wiring lines are increased to drop the production yields due to the closely arranged elements and wiring lines.
The electric method has the highest precision for detecting the positions of defects. If a method in which electric charges are once stored in individual pixels by various writing methods and the amount of the electric charges are read out through a signal line is employed, many difficulties are found for inspecting all the elements and the wiring lines of the pixels, because the elements and the wiring lines are complicated. These difficulties are encountered by the need of sufficient destaticizations before the inspection of minute charge differences or of inordinate amount of time for detecting the malfunctions of individual elements by various writing methods.
Here, the example of a long inspection time is found in a method for inspecting the open/short of switching transistors by measuring the change in a parasitic capacity (as referred to JP-A-2004-347749 (Patent Document 1)) , and the example of an improvement in the detection precision is found in a method for detecting a current flow to be fed to pixel electrodes by forming switches and inspecting wiring lines at the pixel electrodes of individual pixels, that is, the pixels become denser to increase the percent defective (as referred to JP-A-2004-191603 (Patent Document 2)).